Page 194 - Advanced Gas Turbine Cycles

160 Advanced gas turbine cycles

8.7. IGCC cycles with C02 removal (Cycles E)

The IGCC cycle was described in Section 7.4.2. Obviously, there is an attraction in
burning cheap coal instead of expensive gas, but the IGCC plant will discharge as much
carbon dioxide as a normal coal burning plant unless major modifications are made to
remove the C02 (Table 8.1E).
As for the conventional methane burning cycles the IGCC plants can be modified
(a) for addition of C02 absorption equipment in a semi-closed cycle (Cycle El);
(b) for combustion with fuel modification with extra water shift reaction downstream of
the syngas production plant (Cycle E2); and
(c) for combustion with full oxidation of the syngas (Cycle E3).
Fig. 8.24 shows an example of a semi-closed plant (Cycle El) as studied by Chiesa and
Lozza [ 171. The C02 absorption takes place downstream of the HRSG after further cooling
with water removal.
Fig. 8.25 shows an example of the second open type of IGCC plant proposed (Cycle E2)
with an additional shift reactor downstream of the gasifier and syngas cooling and cleansing
plant. Absorption of the C02 is at high pressure which may require physical absorption
equipment of the type described in Section 9.2.2 [3]. However, Manfrida [4] argued that it is
still possible to use chemical absorption at moderately high pressure in this IGCC plant.
Finally, Fig. 8.26 shows Cycle E3-a semi-closed IGCC plant with oxygen fed to the
main syngas combustion process in a semi-closed cycle [18]. Now the exhaust from the
HRSG is cooled before removal of the C02 at low pressure, without need of complex
equipment.

AIR STEAM
SEPARATION
UNIT
T AIR

AIR
T

v
STEAM
CYCLE

WATER

LIQUEFACTION
LIQUID COz
Fig. 8.24. Cycle El. Semi-closed IGCC plant with C02 removal (after Chiesa and Lozza [17]).